Improved Methane Yield Research Articles

Correction: Chow et al. Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield. Processes 2020, 8, 39

The journal is publishing this correction to update the name of the Academic Editor listed on this published paper [...]

Optimized thermal pretreatment for lignocellulosic biomass of pigeon pea stalks to augment quality and quantity of biogas production

By applying heat to the feedstock during the thermal treatment of biomass for the production of biogas, the organic material's biodegradability can be greatly increased. Biogas production is a huge research area for alternate energy production technology. Increased biodegradability, improved methane yield, pathogen, and weed seed destruction, and overall process efficiency are all benefits of this type of pretreatment. It is a useful pretreatment technique for maximizing the production of biogas because it can decrease inhibitory compounds, and increase the digestibility of biomass. This work focused on increasing the efficiency of biogas production from lignocellulosic biomass of pigeon pea stalks by a novel thermal pretreatment. The pigeon pea stalk is initially imposed to physical pretreatment (PT) by an automatic hammer mill which is considered as a base for comparing performance. Thermal pretreatment was carried out for one hour, and two hours durations at different temperatures like 100 °C, 125 °C, 150 °C, 175 °C, and 200 °C. Compared to physically pretreated pigeon pea stalks, 200ᴼC thermal pretreated pigeon pea stalks for two hours have produced 88.41 % higher biogas, 16.14 % increase of cellulose, 19.9 % higher volatile solid removal, and 3.94 % lesser lignin. The enhanced chemical characteristics were ensured by analyzing the chemical composition variations through the FTIR, XRD, and SEM images. So, this is recommended for enhanced biogas production.

Enhancing thermophilic methane production from oil palm empty fruit bunches through various pretreatment methods: A comparative study

This study investigated the effects of various pretreatment methods on the anaerobic digestibility of oil palm empty fruit bunches (EFB) for methane production. Pretreatment methods included weak alkaline (2 % Ca(OH)2), weak acid (2 % acetic acid), acidified palm oil mill effluent (POME), biogas effluent, hydrothermal (180 °C, 190 °C, and 200 °C), and microwave pretreatments. All pretreatment methods enhanced methane yield compared to untreated EFB (189.45 mL-CH4/g-VS), with weak alkaline pretreatment being the most effective (277.11 mL-CH4/g-VS), followed by hydrothermal pretreatment at 180 °C (244.33 mL-CH4/g-VS) and biogas effluent pretreatment (238.32 mL-CH4/g-VS). The enhanced methane yield was attributed to increased cellulose content (45.5 % for weak alkaline pretreatment), reduced hemicellulose (18.0 % for hydrothermal pretreatment at 200 °C), and lignin contents (19.0 % for hydrothermal pretreatment at 200 °C), decreased crystallinity index (40.0 % for hydrothermal pretreatment at 200 °C), and increased surface area. Weak alkaline pretreatment also showed the highest net energy balance (8.73 kJ/g-VS) and a short break-even point (2 years). Microbial community analysis revealed that weak alkaline pretreatment favored the growth of syntrophic acetate-oxidizing bacteria and hydrogenotrophic methanogens, contributing to improved methane yield. This study demonstrates the potential of EFB pretreatment, particularly weak alkaline and biogas effluent pretreatment, for enhancing methane production and sustainable management of palm oil mill waste.

Synergistic effect of biological pre-treatment on co digestion of rice straw and sewage sludge: Process optimization and microbial interactions

The increasing demand for renewable energy sources has prompted a search for innovative and efficient approaches for biogas production. This study investigates the potential of achieving sustainable biogas production through a synergistic combination of biological pre-treatment and co-digestion of rice straw (RS) and sewage sludge (SS). The goal is to enhance the overall methane yield, mitigate substrate limitations, and optimize the biogas production process. In this study, rice straw and sewage sludge were anaerobically co-digested in ratios of 100:0, 70:30, 50:50, 30:70, and 30:70. It was observed that the co-digestion ratio of 70:30 is optimal to achieve maximum methane yield of 0.3 L CH4/(g VS added). Biological pre-treatment with five different organisms Sphingobium sp., Paenibacillus sp., Microbacterium sp., Pseudomonas sp., and Stenotrophomonas sp. was also examined for RS and co-digested with SS at the optimized ratio to improve the degradability of RS. This pre-treatment strategy is anticipated to enhance the accessibility of microorganisms to substrates and accelerate the rates of hydrolysis. The biological pre-treatment resulted in a 20–23% improvement in methane yield compared to untreated substrates. Metagenomic studies revealed the dominance of Bacteroidetes, Firmicutes, and Proteobacteria, which are capable of utilizing lignocellulosic biomass and ultimately converting it to methane. The acetoclastic methanogensis is the major methane generating pathway which is supported by the complete dominance of genus Methanosaeta.

Model based analysis of trace metal dosing strategies to improve methane yield in anaerobic digestion systems

Favourable effects of trace metals (TMs) on regulating anaerobic digestion (AD) performance are extensively utilised to improve methane yield. This study discusses a model-based approach to find out the best TM dosing strategies. The model has been applied to compare continuous, preloading, pulse dosing and in-situ loading. Simulations were also carried out to comprehend appropriate dosing form, dosing time and quantity of metals to be dosed. Model results show that the best way to dose TMs is repeated pulse dosing at low concentration levels in the optimum range with high frequency. Best dosing strategy for the system in this study was found to be 5 µM pulse loading at 5 days intervals as it gave maximum methane production and low effluent metal loss. Preferable dosing form depends on reactor configuration and this has been verified after model calibration with experimental data. Easily dissociable metal chlorides are ideal for continuous reactors.

Research Progress of Antibiotic Resistance Genes Removal in Food Waste During Anaerobic Digestion

Food waste is one of the important reservoirs of antibiotic resistance genes （ARGs）, and its resource utilization has potential environmental risks. Anaerobic digestion （AD） technology can concurrently achieve resource recovery and ARGs removal, which is one of the popular resource technologies for food waste management. However, the removal efficiency of ARGs during the AD process is limited, and thus the safety of digestate for agricultural use is still questioned. Therefore, how to improve the performance of ARGs removal during the AD process is critical for efficient and environmentally friendly bioconversion of food waste. This study summarized the transmission pathways and mechanisms of ARGs in food waste； discussed the effects of different operation parameters on the transmission of ARGs in food waste during the AD process； described the research progress of exogenous addition of conductive materials, feedstock pretreatment, etc., strategies to enhance the removal of ARGs； and analyzed the migration regularity and removal mechanism of ARGs in food waste during the AD process, which mainly included microbial community structure evolution, mobile genetic element changes, and environmental factor changes. Finally, this study prospected the future improvement of methane yield and ARGs removal in the AD process of food waste based on the existing research.

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Impact of tannery wastes on anaerobic co-digestion: enhancing biogas production and process efficiency

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry.Graphical

Preliminary analysis: Effect of a rotary generator of hydrodynamic cavitation on rheology and methane yield of wastewater sludge

Slightly acidic (pH 5.1) waste sludge with 4.7 % Total Solids (TS) was treated on a laboratory scale pined disc rotary generator of hydrodynamic cavitation (PD RGHC). Influence of four rotor discs with different number of cavitation generation units (CGUs) was investigated: 8-pins, 12-pins, 16-pins and 8-prism elements. The effect of hydrodynamic cavitation (HC) was investigated by analyzing rheological properties, surface tension, dewaterability, and particle size distribution. After subjecting the sludge to 30 cavitation passes, the dewatering ability of the sludge significantly decreased, resulting in a more than two-fold increase in Capillary Suction Time (CST). All regimes were successful in disintegrating particles to smaller sizes. A slight increase of sludge surface tension was measured post cavitation. Cavitated samples displayed a zero-shear viscosity, in contrast to the untreated sample, where viscosity noticeably increased as shear stress decreased. HC did not improve methane yield. Statistically significant correlations between physio-chemical properties and apparent viscosity at low shear stress were identified. Although there were no discernible statistical differences in sludge characteristics, some trends are visible among investigated CGU designs and warrant further research.

Magnetite modified zeolite as an alternative additive to promote methane production from anaerobic digestion of waste activated sludge

Methane recovery from bio-wastes is one promising renewable energy to relieve the energy crisis faced around the world. Zeolite is one of attractive exogenous additives for promoting methane production from anaerobic digestion due to its potentials in regulating microorganism enrichment and anaerobic environment. However, the poor electron mediated ability limited its positive effects. Hence, this study hypothesized that the electron mediated ability of zeolite would be improved by loading magnetite, thereby generating more positive impacts on the performance of sludge anaerobic digestion. Compared to control group, magnetite modified zeolite (MZ) effectively improved methane yield by 37.4%. The reason was that the electron mediated ability and adsorption capacity of zeolite were improved by loading magnetite, facilitating the degradation of refractory organics and the conversion of volatile fatty acids. Moreover, the activities of cytochrome c and F420 increased by 33.3% and 29.8% with MZ additive, contributing to stimulating efficient electron transfer process. In addition, the electro-active genera were enriched, such as Bacteroidetes_vadinHA17, Methanobacterium, and Methanosaeta, and the direct interspecies electron transfer was possibly established for methanogenesis with the help of MZ. This study will provide valuable references for the application of zeolite in anaerobic digestion.

Enhancing Methane Yield in Anaerobic Co-Digestion of Primary Sewage Sludge: A Comprehensive Review on Potential Additives and Strategies

Traditionally, anaerobic digestion has been applied to mixed sludge, combining primary sludge (PS) with secondary sludge. However, recent research has unveiled the advantages of dedicated PS digestion due to its higher energy content. Anaerobic digestion (AD) of primary sewage sludge can offer a sustainable solution for managing sewage sludge while generating renewable energy. The present study provides a comprehensive examination of the current state of knowledge regarding the anaerobic digestion of PS. Co-digestion of PS with organic substrates, including food waste and agro-industrial residues, emerges as a promising approach to boost biogas production. Additionally, the utilization of additives such as glucose and clay minerals has shown potential in improving methane yield. Critical factors affecting AD, such as pretreatment methods, carbon-to-nitrogen (C/N) ratio, temperature, pH, volatile fatty acids (VFAs) levels, organic loading rates (OLR), inoculum-to-substrate ratio (ISR), and the role of additives, have been meticulously studied. Finally, this review consolidates existing knowledge to advance our understanding of primary sewage sludge anaerobic digestion, fostering more efficient and sustainable practices in sludge management and renewable energy generation.

Co-digestion potential of different industrial sludge sources and impact on energy recovery

Co-digestion potential of the wastewater treatment sludges produced at two industries with different characteristics was investigated in anaerobic batch reactors operated at mesophilic (35±2 °C) condition. The sludge sources selected were from a food industry producing edible oil and from a textile industry producing woven fabric. Reactor performance was evaluated by the conventional parameters as well as by monitoring the biogas production during co-digestion of both industrial sludges at equal mixing proportions. Results indicated that both of these sludge sources had substantial biogas production potential with a cumulative biogas yield more than 425 mL/g-VSSfed whereas it was about 5-fold lower only for the food sludge. On the other hand, chemical oxygen demand (COD) removal reached to about 90% during co-digestion with a well recovery of pH value and alkalinity concentration for sufficient buffering at the end of incubation. Therefore, by the combination of different industrial sludges through co-digestion; higher digestion performance and improved methane yield could be achieved due to better balanced substrate and nutrients. Regarding the initial heavy metals in the supernatant phase of the mixed sludge; iron (Fe), zinc (Zn), nickel (Ni), aluminum (Al), and manganese (Mn) could be removed from 56% to 80% while no apparent removals were observed in cadmium (Cd) and lead (Pb) at the end of operation. Hence, these potential toxic pollutants in the digestate should be taken into consideration while deciding the most appropriate resource recovery and ultimate disposal methods.

Mitigating short-circuits through synergistic temperature and hydraulic retention time control for enhancing methane yield in continuous stirred-tank reactors

Temperature and hydraulic retention time (HRT) control are crucial for mitigating the “short-circuit” issue and enhancing methane production in continuous stirred-tank reactors. This study focuses on the combined effects of temperature and HRT on methanation via operating the reactors at different temperatures (35 °C, 45 °C, and 55 °C) and HRT (30, 25, and 20 d) for 116 days. The results demonstrated that the digester conducted at 45 °C and an HRT of 30 d unexpectedly yielded the maximum average methane production of 296.08 ml/g volatile solids (VS). In contrast, the optimal HRT for the 35 °C and 55 °C digesters were 25 and 30 d, with a methane yield of 241.88 ml/g VS and 240.9 ml/g VS, respectively. High-throughput sequencing shows that Firmicutes, Bacteroidetes, Themotogae, Chloroflexi, and Acidobacteria dominated 90–98 % of the total bacteria. Temperature exhibited a significant influence on shaping microbial ecosystems, indicating that temperature, rather than HRT, is the primary factor to consider. Additionally, metagenomic analysis reveals that the levels of genes involved in acetoclastic and hydrogenotrophic methanogenic pathways were enhanced at 45 °C, probably improving methane yield. These findings provide new insights into “short-circuit” mitigation and strategies to strengthen methane generation from biomass.

Enhanced Anaerobic Digestion Using Conductive Materials through Mediation of Direct Microbial Interspecies Electron Transfer: A Review

The anaerobic digestion (AD) of organic matter is susceptible to the challenges posed by low-speed electron transfer between microorganisms and the limitation of low hydrogen partial pressure, resulting in low methane recovery efficiency and poor system stability. Numerous studies in recent years have shown that a variety of conductive materials can significantly increase the interspecies electron transfer (IET) rate, optimize the structure and function of anaerobic microbial communities, improve methane yield, and promote system stability by mediating the direct interspecies electron transfer (DIET) of reciprocal microorganisms. In this study, on the basis of investigating the IET mechanism of methanogenic microorganisms in the AD of organic matter, the effects of carbon-based conductive materials (activated carbon, biochar, carbon cloth, carbon fiber, graphite, graphite felt, graphene, and carbon nanotubes) and iron-based conductive materials (magnetite, Fe3O4, hematite, Fe2O3, goethite, and zero-valent iron) on AD performance and microbial community using DIET are reviewed. Future research should focus on establishing an evaluation system, identifying flora with DIET potential, and finding methods for engineering applications that increase recovery efficiency and reveal the principle of conductive materials to mediate DIET.

Advanced steam-explosion pretreatment mediated anaerobic digestion of municipal sludge: Effects on methane yield, emerging contaminants removal, and microbial community

Advanced steam explosion pretreatment, i.e., the Thermal hydrolysis process (THP) is applied mainly to improve the sludge solubilization and subsequent methane yield in the downstream anaerobic digestion (AD) process. However, the potential of THP in pretreating the high solids retention time (SRT) sludges, mitigating the risk of emerging organic micropollutants and effects on anaerobic microbiome in digester remains unclear. In this study, sludge from a sequencing batch reactor (SBR) system operating at a SRT of 40 days was subjected to THP using a 5 L pilot plant at the temperature ranges of 120–180 °C for 30–120 min. The effect of THP on organics solubilization, methane yield, organic micropollutant removal, and microbial community dynamics was studied. The highest methane yield of 507 mL CH4/g VSadded and volatile solids (VS) removal of 54% were observed at 160°C- 30min THP condition, i.e., 4.1 and 2.6 times higher than the control (123 mL CH4/gVSadded, 20.7%), respectively. The experimental values of hydrolysis coefficient and methane yield have been predicted using Modified Gompertz, First order, and Logistics models. The observed values fitted well with all three models showing an R2 value between 0.96 and 1.0. THP pretreated sludges showed >80% removal of Trimethoprim, Enrofloxacin, Ciprofloxacin, and Bezafibrate. However, Carbamazepine, 17α-ethinylestradiol, and Progesterone showed recalcitrant behavior, resulting in less than 50% removal. Microbial diversity analysis showed the dominance of Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes, collectively accounting for >70–80% of bacterial reads. They are mainly responsible for the fermentation of complex biomolecules like polysaccharides, proteins, and lipids. The THP-mediated anaerobic digestion of sludge shows better performance than the control digestion, improved methane yield, higher VS and micropollutants removal, and a diverse microbiome in the digester.

Hydrothermal and thermal-acid pretreatments of wheat straw: Methane yield, recalcitrant formation, process inhibition, kinetic modeling

Bio-methanation of agro-residue could fulfill the rising energy demands and curb the environmental pollution. Nevertheless, hydrolysis is the rate limiting step in anaerobic digestion (AD) of agro-waste (wheat straw, WS) due to its recalcitrant lignocellulosic composition. Hydrothermal (100–175 °C, 30–120 min) and thermal-acid (100–175 °C, 0.5–2% H2SO4 v/v) pretreatments of WS were performed to assess the pretreatment effects on WS solubilization, recalcitrant formation, lignocellulosic composition and improvement in methane yield. The 60-min hydrothermal pretreatments had an optimum chemical oxygen demand (COD) solubilization. The hydrothermal pretreatment degraded predominantly the hemicellulose by 53.4%. The furan derivatives, i.e., furfural and 5-hydroxyl-methyl-furfural (5-HMF) were formed during hydrothermal pretreatment of WS at 175 °C. The furfural and 5-HMF were generated at all studied thermal-acid pretreatment conditions owing to hemicellulose solubilization. The anaerobic co-digestion (AcoD) of hydrothermally and thermal-acid pretreated WS was performed with food waste and cow manure in a batch assay. The hydrothermally pretreated WS showed 4–14% higher methane production, while the thermal-acid pretreated WS had 29–44% less methane production than untreated WS. High concentrations of furfural, 5-HMF, total volatile fatty acids (tVFA), and NH4–N affected the methane production in digesters treating thermal-acid pretreated WS. The kinetic analysis of the assays revealed that methane production was affected by furfural, 5-HMF, temperature and acid dosing. Therefore, the calculated values through modified Gompertz and logistic models deviated from the experimental values.

Monitoring of a microbial community during bioaugmentation with hydrogenotrophic methanogens to improve methane yield of an anaerobic digestion process

Methane production by microbial fermentation of municipal waste is a challenge for better yield processes. This work describes the characterization of a hydrogenotrophic methanogen microbial community used in a bioaugmentation procedure to improve the methane yield in a thermophilic anaerobic process, digesting the organic fraction of municipal solid waste. The performance of the bioaugmentation was assessed in terms of methane production and changes in the microbial community structure. The results showed that bioaugmentation slightly improved the cumulative methane yield (+ 4%) in comparison to the control, and its use led to an acceleration of the methanogenesis stage. We observed associated significant changes in the relative abundance of taxa and their interactions, using high throughput DNA sequencing of V3-16S rRNA gene libraries, where the abundance of the archaeal hydrogenotrophic genus Methanoculleus (class Methanomicrobia, phylum Euryarchaeota) and the bacterial order MBA08 (class Clostridia, phylum Firmicutes) were dominant. The relevant predicted metabolic pathways agreed with substrate degradation and the anaerobic methanogenic process. The purpose of the study was to evaluate the effect of the addition of hydrogenotrophic methanogens in the generation of methane, while treating organic waste through anaerobic digestion.

The role of biochar in the psychrophilic anaerobic digestion: Effects on kinetics, acids metabolism, and microbial population

This study investigated the effect of biochar in the psychrophilic anaerobic co-digestion regarding biomethane production potential (BMP), metabolic efficiencies, and microbial population. BMP tests of cheese whey and cattle manure as substrates were conducted at different gasified pine wood biochar concentrations (Bc) (10 g/L, 30 g/L, 50 g/L); and particle sizes (Ps) (~0.15 mm, ~0.575 mm, ~1 mm). The most favourable conditions of Ps = 0.575 mm and Bc of 30 g/L, allowed BMP values to go from 0.23 m3 CH4/kg VSadd to 0.34 m3 CH4/kg VSadd. The study of metabolic stages showed how the biochar modulates hydrolysis and methanogenesis and favours the acetoclastic metabolism to improve methane yield even at 15 °C. The biochar's positive effect is reinforced by its addition boosting the growth of methanogen psychrotrophs populations up to 520 % compared with a BMP with no biochar added at 15 °C. The study showed that psychrophilic AD + biochar might overcome mesophilia's energy needs by improving yields with no extra energetic requirements.

Mechanistic insights into Fe3O4-modified biochar relieving inhibition from erythromycin on anaerobic digestion

Anaerobic digestion (AD) of antibiotic manufacturing wastewater to degrade residual antibiotics and produce mixture of combustible gases has been investigated actively in the past decades. However, detrimental effect of residual antibiotic to microbial activities is commonly faced in AD process, leading to the reduction of treatment efficiency and energy recovery. Herein, the present study systematically evaluated the detoxification effect and mechanism of Fe3O4-modified biochar in AD of erythromycin manufacturing wastewater. Results showed that Fe3O4-modified biochar had stimulatory effect on AD at 0.5 g/L erythromycin existence. A maximum methane yield of 327.7 ± 8.0 mL/g COD was achieved at 3.0 g/L Fe3O4-modified biochar, leading to the increase of 55.7% compared to control group. Mechanistic investigation demonstrated that different levels of Fe3O4-modified biochar could improve methane yield via different metabolic pathways involved in specific bacteria and archaea. Low levels of Fe3O4-modified biochar (i.e., 0.5–1.0 g/L) led to the enrichment of Methanothermobacter sp., strengthening the hydrogenotrophic pathway. On the contrary, high levels of Fe3O4-modified biochar (2.0–3.0 g/L) favored the proliferation of acetogens (e.g., Lentimicrobium sp.) and methanogen (Methanosarcina sp.) and their syntrophic relations played vital role on the simulated AD performance at erythromycin stress. Additionally, the addition of Fe3O4-modified biochar significantly decreased the abundance of representative antibiotic resistant genes (ARGs), benefiting the reduction of environmental risk. The results of this study verified that the application of Fe3O4-modified biochar could be an efficient approach to detoxify erythromycin on AD system, which brings high impacts and positive implications for biological antibiotic wastewater treatment.

Investigates of substrate mingling ratio and organic loading rate of KOH pretreated corn stover and pig manure in batch and semi-continuous system: Anaerobic digestion performance and microbial characteristics

The effects of substrate mingling ratio (SMR) (1:1, 1:2, 1:3, 3:1, and 2:1) and organic loading rate (OLR) (50–90 g total solids per liter per day) on anaerobic co-digestion performance and microbial characteristics were investigated for pig manure (PM) and pretreated/untreated corn stover in batch and semi-continuous anaerobic digestion (AD) system. The results showed that SMR and pretreatment affected co-digestion performance. The maximum cumulative methane yield of 428.5 ml⋅g−1 (based on volatile solids (VS)) was obtained for PCP13, which was 35.7% and 40.0% higher than that of CSU and PM. In the first 5 days, the maximum methane yield improvement rate was 378.1% for PCP13. The daily methane yield per gram VS of PCP13 was 11.4%–18.5% higher than that of PCU13. Clostridium_sensu_stricto_1, DMER64, and Bacteroides and Methanosaeta, Methanobacterium, and Methanospirillum had higher relative abundance at the genus level. Therefore, SMR and OLR are important factor affecting the AD process, and OLR can affect methane production through volatile fatty acids.